500 research outputs found
Representation of the pulsed output from a mode-locked laser using quantum field theory and an application in multiphoton ionisation
Critical Behavior of Light
Light is shown to exhibit critical and tricritical behavior in passive
mode-locked lasers with externally injected pulses. It is a first and unique
example of critical phenomena in a one-dimensional many body light-mode system.
The phase diagrams consist of regimes with continuous wave, driven para-pulses,
spontaneous pulses via mode condensation, and heterogeneous pulses, separated
by phase transition lines which terminate with critical or tricritical points.
Enhanced nongaussian fluctuations and collective dynamics are observed at the
critical and tricritical points, showing a mode system analog of the critical
opalescence phenomenon. The critical exponents are calculated and shown to
comply with the mean field theory, which is rigorous in the light system.Comment: RevTex, 5 pages, 3 figure
International medical students’ expectations and worries at the beginning of their medical education: a qualitative focus group study
Background: The number of international students has increased substantially within the last decade. Due to cultural barriers, this specific group faces diverse challenges. In comparison to German colleagues, international medical students perform significantly lower in clinical examinations and exceed the average duration of study; they suffer from personal distress as well as insufficient support. Within the present study, their individual perspectives, expectations, hopes and fears were examined. Methods: Four focus groups with first-year international medical students (N = 16) were conducted in October 2013. Each 60- to 90-min discussion was audiotaped, transcribed and analysed using qualitative methods. Results: International medical students go abroad in search of good study-conditions. For the choice of place of study, affordability, social ties as well as an educational system following the achievement principle are decisive factors. While contact with German-students and other international students is seen as beneficial, international medical students are most concerned to encounter problems and social exclusion due to language deficits and intercultural differences. Conclusions: Facilitating the access to university places, the provision of financial aid and, moreover, social support, nurturing cultural integration, would greatly benefit international medical students. Hereby, the establishment of specific medical language courses as well as programs fostering intercultural-relations could prove to be valuable
Optical frequency synthesizer with an integrated erbium tunable laser.
Optical frequency synthesizers have widespread applications in optical spectroscopy, frequency metrology, and many other fields. However, their applicability is currently limited by size, cost, and power consumption. Silicon photonics technology, which is compatible with complementary-metal-oxide-semiconductor fabrication processes, provides a low-cost, compact size, lightweight, and low-power-consumption solution. In this work, we demonstrate an optical frequency synthesizer using a fully integrated silicon-based tunable laser. The synthesizer can be self-calibrated by tuning the repetition rate of the internal mode-locked laser. A 20 nm tuning range from 1544 to 1564 nm is achieved with ~10-13 frequency instability at 10 s averaging time. Its flexibility and fast reconfigurability are also demonstrated by fine tuning the synthesizer and generating arbitrary specified patterns over time-frequency coordinates. This work promotes the frequency stability of silicon-based integrated tunable lasers and paves the way toward chip-scale low-cost optical frequency synthesizers
Analysis of transfer genes and gene products within the traB-traC region of the Escherichia coli fertility factor, F.
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Experimental Implementation of Optical Clockwork without Carrier-Envelope Phase Control
We demonstrate an optical clockwork without camer-envelope phase control using sum-frequency generation between a CW optical parametric oscillator at 3.39 μm and a modelocked Tisapphire laser with dominant spectral peaks at 834 and 670 nm
Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb
We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.Comment: 18 pages, 4 figure
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Optical Clockwork without Carrier-Envelope Phase Control
We demonstrate optical clockwork without carrier-envelope phase control using sum-frequency generation between a cw optical parametric oscillator at 3.39 μm and a mode-locked Ti:sapphire laser with dominant spectral peaks at 834 nm and 670 nm
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